A hydraulic unit of this kind is known from DE 10 2008 002 740 A1, for example. This known hydraulic unit has a housing block, on which the individual components for controlling the brake pressure in accordance with the existing wheel slip are arranged and hydraulically interlinked. One essential component for this is a pump, which is inserted into a pump receptacle of the housing block and is actuated, e.g. mechanically by an electric motor and an eccentric driven by the latter. Pumps pump pressure medium away from the wheel brakes when required in order to lower the wheel brake pressure or supply pressure medium to the wheel brakes at a high pressure if an increase in the wheel brake pressure is necessary.
Particularly pumps in the form of piston pumps can trigger pressure pulsations owing to the cyclical operating principle thereof, and these pulsations are perceptible as unwanted operating noise in the vehicle. To smooth or damp these pulsations, damping devices are provided on the pump pressure side, said devices generally having at least one pressure medium accumulator with an accumulator capacity (C element) that can vary in accordance with the pressure and at least one restriction element (R element), which is arranged downstream thereof. Spring-operated piston accumulators as pressure medium accumulators are known, for example, said accumulators being arranged in a dedicated accumulator receptacle of the hydraulic unit and being linked to the pump pressure side by pressure-medium-carrying fluid ducts. Known restriction elements include fixed restrictors with a constant restrictor cross section or dynamic restrictors with a restrictor cross section that can vary in accordance with the pressure.
Irrespective of this, the small amount of installation space available in motor vehicles makes it necessary to embody the hydraulic unit and hence the housing block thereof in as compact and weight-saving a manner as possible. One known measure for this is to arrange the fluid duct for linking a switchover valve to an inlet valve of a vehicle brake system on the hydraulic unit in such a way that it intersects a pump receptacle.
If a damping device is then connected to a fluid duct routed in this way in order to damp pressure pulsations, there is then the disadvantage that the restriction element arranged downstream of the pressure medium accumulator represents a flow resistance which has a disadvantageous effect in operating states of the vehicle brake system in which it is important to supply as large as possible a pressure medium volume quickly. These are, for example, emergency braking operations, especially those for avoiding a collision with other road users. Particularly in the case of falling temperatures and, accordingly, increasingly viscous pressure medium, the restricting effect of the restriction element furthermore increases sharply and thereby exacerbates the effect described.